DESCRIPTION: Arterial smooth muscle cells (SMC) are ordinarily in a contractile, nonproliferative state. Arterial injury can cause SMC to undergo an activation into a proliferative state. cAMP and cGMP inhibit proliferation and SMC are constantly exposed to agents elevating these mediators, therefore enhanced degradation of cAMP and cGMP are necessary. The investigators have hypothesized that in human SMC, a new phosphodiesterase (PDE1C) must be induced to degrade cyclic nucleotides. This application focuses on determination of the role of PDE1C in SMC proliferation. The investigators propose to study this in four specific aims. Aim 1 asks the question whether PDE1C is restricted to proliferating SMC. The underlying hypothesis is that PDE1C will be highly expressed in proliferating, synthetic SMC in vitro and in normal and disease processes characterized by increased SMC proliferation (atherosclerotic lesions, neonatal pulmonary hypertension, balloon angioplasty) in human or ovine tissue. Conversely, quiescent cells should express little PDE1C. Aim 2 addresses the potential importance of the extracellular matrix in regulation of PDE1C expression. Arterial lesions may expose SMC to various components of the extracellular matrix and preliminary studies suggest monomer collagen can upregulate PDE1C, while fibrillar collagen does not have this effect. In this aim, the investigators will study the effect of various components of the extracellular matrix on PDE1C expression. They will also determine the role of the p70 S6 kinase pathway which is known to be regulated by extracellular matrix. Aim 3 will delineate what regions in the PDE1C promoter confer sensitivity to extracellular matrices and intracellular signals induced by these matrices. Cloning of the human SMC PDE1C and its promoter region and generation of truncated promoter sequences coupled to reporter constructs will provide information about sequences regulating PDE1C expression. Aim 4 will ask the question of whether PDE1C is required for SMC proliferation. PDE1C will be inhibited using pharmacologic inhibitors as well as antisense mRNA of the enzyme. Change in SMC phenotype to the proliferative state in cells overexpressing PDE1C will be determined. Inhibitors of PDE1C should conversely, prevent SMC proliferation.